Groundwater pesticides: interactive effects of low concentrations of carbamates aldicarb and methomyl and the triazine metribuzin on thyroxine and somatotropin levels in white rats.

Using full-factorial design experiments for three variables at two levels each and center replicates, we examined the effects of common agricultural carbamate insecticides, aldicarb and methomyl, and a triazine herbicide, metribuzin, on hormone levels in Sprague-Dawley rats. Fifty-four female rats were sampled at 2 and 6 wk during a 6-wk exposure to individual chemicals or to combinations of them. Some main effects and interaction effects were significant. For example, rats treated with the herbicide (metribuzin) were hyperthyroid. The interactions of all three chemicals also significantly increased thyroxine levels. One year later, we repeated these experiments for 16 wk using 54 male rats; the results were very similar. Metribuzin alone significantly increased thyroxine throughout the second study (at 7, 13, and 16 wk). Somatotropin levels were significantly altered after 13 wk of exposure. The same concentrations and mixtures of these three pesticides have now been shown to be implicated in learning impairment and other neurological functions, immune parameter changes, and endocrine changes. These findings support the concept of the interconnectedness of the nervous, endocrine, and immune systems and raise the likelihood of impacts on all three systems if one is shown to be affected. Development, growth, and reproduction all depend on the proper function of these three systems. These results strongly suggest the need to reassess currently allowed "safe" levels of chemicals based on adult dosages that are accepted in ground-water and in our food supplies.